Michaelsen, 1923
Description
Transparent worms. Eyes present. Dorsal bundles beginning from VI, with one 180-310 µm long hair chaeta and 1-2 blunt, 55-85 µm long needle chaetae. In needle chaetae nodulus at 1/5-1/4 from distal end. Ventral chaetae in II-V by 4-10, about 120 µm long, slender, with long sickle-shaped upper tooth and much shorter, sometimes reduced, lower tooth clinging to it. Beginning from VI ventral chaetae by 2-7, shorter (80-90 µm) and much thicker, their upper tooth twice as long as lower one but equally thick. In mature individuals penial chaetae by 2-4. Stomachal dilatation abrupt. Length 3-5 mm, segment number in zooids up to 28, in single individuals 28-36. Similar (and probably closely related) to Nais alpina but with finer and very strongly curved teeth in anterior ventral chaetae, lower teeth often more or less reduced.
Crawling on substratum.
Distribution
Holarctic.
Ecology
In freshwater, mostly in large rivers on sand.
Reproduction
Mostly asexual, by paratomy (budding). Mature individuals and sexual reproduction rare or seasonal.
Literature
Michaelsen, 1923: 34-37, Fig.; Sperber, 1948: 119-120, Fig. 12B; Sperber, 1950: 63, Fig. 13; Brinkhurst and Jamieson, 1971: 340-341, Fig. 7.7J-N; Chekanovskaya, 1981: 227-229, Fig. 99; Hrabe, 1981: 48-49, Pl. 7 Figs 10-14; Kasprzak, 1981: 118-119, Figs 314-319.